This invention relates to a self-processing photographic film unit, and more particularly to a trap member for catching surplus processing solution.
A self-processing photographic film unit (hereinafter, a film unit) which commonly is called an instant film, as shown in FIG. 7, includes a photosensitive sheet 1 having a photosensitive layer and an image receiving layer, a transparent coVer sheet 2, and a mask sheet 3. The mask sheet 3 has an exposure opening 3A and is attached to the photosensitive sheet 1 in such a manner as to block the opening 3A from the back. Also, the mask sheet 3 and the cover sheet 2 are attached through a spacer rail 4, thereby to form a predetermined distance between the photosensitive sheet 1 and the cover sheet 2.
The front end portion of the mask sheet 3 is folded back inwardly in order to wrap a processing solution container 5 which stores processing solution. The edge of the front end portion is attached to the surface of the cover sheet 2. The rear end portion of the mask sheet 3 is folded back inwardly in order to wrap a trap member 6 for catching surplus processing solution. The edge of the rear end portion is attached to the cover sheet 2. The foregoing arrangement forms a trap section 7 for storing the trap member 6 and catching the surplus processing solution. A more detailed description of the construction of this film unit is provided, for example, in Japanese Patent Laid-open Publication No. Sho 62-91940.
As is known, a film unit is loaded in an instant camera, and the photosensitive sheet 1 is exposed by light passed through the exposure opening 3A when the shutter is operated. After exposure, the film unit is passed between a pair of processing solution developing rollers with its front end 8A ahead, and is discharged from the instant camera. The processing solution developing rollers pressurize the processing solution container 5, push out the processing solution stored therein, and spread it in a space formed between the photosensitive sheet 1 and the cover sheet 2 over a uniform width. The photosensitive sheet 1 is processed by such spread processing solution, and as a result, a positive image appears on its back side.
When the processing solution is being spread, surplus processing solution enters the trap section 7 and is caught by the trap member 6 contained therein. Just when the surplus processing solution is processed, air contained in the space also is pushed, flows out toward the trap portion 7 together with the surplus processing solution, and then is discharged through a plurality of air discharging holes 9 which are formed in the mask sheet 3.
Examples of the trap section are disclosed in at in U.S. Pat. Nos. 2,627,460, 3,589,904, 3,615,540, and 3,619,193. The described trap structures are improved in that they enhance smooth discharge of air, but are not intended to ensure perfect protection from leakage of the surplus processing solution caused by various conditions resulting from using the camera or preserving the film unit after taking pictures. Therefore, when processing is performed under summertime conditions, when the temperature is 40.degree. C. and the relative humidity is 90%, surplus processing solution may leak out through air discharging holes.
Also, in a film unit disclosed in Japanese Patent Laid-open Publication No. Sho 52-11027, if the film unit is kept at a temperature of 60.degree. C. and a relative humidity of 80%, the surplus processing solution becomes fluid. As a result, part of the surplus processing solution leaks from the trap section into the exposure opening. An image dye precursor contained in the photosensitive layer is decomposed and scattered with the leaked surplus processing solution, and a change of color occurs in a frame portion of an image forming plane defined with the edge of the exposure opening. The change of color problem in the frame portion also occurs in a trap structure comprising a water absorption layer, a neutralization layer connected therewith, and a plastic net connected with them.
Also, Japanese Patent Laid-open Publication No. Sho 60-140336 describes the use of a water soluble matrix as a trap member, so that the effective catching quantity of the surplus processing solution is increased without increasing the thickness of the trap structure, in order to prevent leakage of the surplus processing solution from the air holes. Although this film unit is capable of preventing leakage when the processing solution is spread, leakage sometimes occurs from discharge air holes when a strong pressure is applied to the trap section.